Golf ball manufacturing method

ABSTRACT

The invention provides a method of manufacturing a golf ball having a core and a cover of one or more layer over the core, wherein an outermost layer of the cover is molded of a thermoplastic material selected from the group consisting of polyurethane, polyurea and mixtures thereof. The method includes at least the following steps (1) and (2):
         (1) treating a surface of the cover with an isocyanate compound; and   (2) washing off and physically removing excess isocyanate compound by blasting the cover surface with a specific substance at high pressure.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of copending application Ser.No. 14/729,207 filed on Jun. 3, 2015, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method of manufacturing a golf ballhaving a cover made of a thermoplastic material, which ball, owing tothe application during ball production of a specific treatment to thesurface of the cover molded from the thermoplastic material, has anexcellent scuff resistance, excellent spin properties and a good ballappearance.

The use of polyurethane materials as golf ball cover-forming materialshas attracted attention in recent years. Polyurethane materials, interms of the molding method used to obtain moldings therefrom, arebroadly divided into thermoset polyurethane materials and thermoplasticpolyurethane materials.

However, moldings of thermoset polyurethane materials have no plasticitywhen heated, and so the feedstock and molded articles made therewithcannot be recycled. Moreover, in the production of such moldings, thethermosetting step and the cooling step take a long time, in addition towhich the feedstock has a high reactivity when heated and is thusunstable, making the molding time very difficult to control. Hence, theproductivity of thermoset polyurethane materials when used to makespecial moldings such as golf ball covers (moldings which encase a corematerial) is regarded as poor.

By contrast, moldings of thermoplastic polyurethane materials are notobtained by the direct reaction of a feedstock; instead, a linearpolyurethane material synthesized by using starting materials and aproduction process which differ somewhat from the foregoing thermosetpolyurethane materials are used in molding. Such polyurethane materialsare thermoplastic; thermoplasticized polyurethane materials have thequality of hardening on cooling. Therefore, it is possible to mold suchpolyurethane materials using an injection molding machine. The injectionmolding of thermoplastic polyurethane materials is ideal as a method formolding golf ball covers, both because the molding time is very shortcompared with the molding time for thermoset polyurethane materials andbecause this method is suitable for precision molding. Also,thermoplastic polyurethane materials are recyclable and thus friendly tothe global environment.

JP-A 2002-336378 describes a golf ball obtained using a cover materialcomposed of a thermoplastic polyurethane material and an isocyanatemixture. The cover material is a thermoplastic polyurethane materialthat is recyclable and moreover has a high resilience and an excellentscuff resistance. This cover material has both the good productivity ofa thermoplastic polyurethane and also exhibits physical propertiescomparable with those of a thermoset polyurethane. At the same time,owing to the plasticizing effect of the isocyanate compound, such anapproach enhances the flowability of the thermoplastic polyurethanematerial and is thus able to improve productivity. Although this art isoutstanding in the above respects, because burn contaminants arise dueto direct charging of the isocyanate mixture into the molding machineand there is some variability in the compounding ratio owing to the useof dry blending, the uniformity is poor, giving rise to moldinginstability. At the same time, the compositional ratio within theisocyanate mixture between the isocyanate compound and the thermoplasticresin that is substantially non-reactive with isocyanate has alreadybeen set, and so one has less freedom of choice in the amounts and typesof isocyanate compound and thermoplastic resin to be added.

JP 5212599 describes a golf ball which has a high rebound and anexcellent spin performance and scuff resistance, and also has a highcover material flowability and a high productivity. However, thethermoplastic polyurethane material used in this art is a special resinmixture, and there are certain challenges associated with theproduction, supply and cost of such resin mixtures. Moreover, becausethis art entails charging an injection molding machine and ancillaryequipment with a material in which isocyanate groups remain in anunreacted state, undesirable effects such as seizing and solidificationdue to deposition of the isocyanate ingredient arise and can cause anincrease in the percent defective.

JP 3494441 discloses art which, in a golf ball having a cover made ofthermoplastic resin, subjects the surface layer of the cover tomodification treatment, thereby giving a cover having excellentproperties. Although this is an excellent approach that enables theproperties to be modified after the cover has been molded from athermoplastic material of excellent moldability, there remains room forimprovement in the degree to which the scuff resistance is enhanced andin the golf ball properties following modification. Particularly incases where 4,4′-diphenylmethane diisocyanate (MDI) has been selected asthe polyisocyanate compound, the MDI must be held at the solidifyingpoint (about 39° C.) or higher in order to place it in a molten liquidstate suitable for treatment. In the case of MDI, production of thedimer also requires care; that is, dimer production generally speeds upat a higher temperature, and so close temperature control is required toensure stable productivity, which can be troublesome. When an ionomermaterial is used in part of the golf ball, there is also a possibilitythat treatment at a high temperature will give rise to deformation or achange in properties.

JP 4051374 describes a method of manufacturing golf balls produced witha thermoplastic polyurethane, polyurea or mixed material thereof havinga high melt index. More specifically, this method includes the step ofobtaining a base thermoplastic polyurethane, polyurea or mixed materialthereof; the step of raising the melt index of this base resin material;the step of molding the thermoplastic polyurethane material having anincreased melt index in a mold; and the subsequent step of treating themolded material with a secondary curing agent such as an isocyanatesolution. This art is outstanding in that, by crosslinking the covermaterial using an isocyanate ingredient, resistance to damage can beimparted while maintaining the other desirable characteristics of thecover, such as a soft feel. However, in cases where the secondary curingagent includes an organic solvent capable of causing the cover materialto swell, depending on the treatment conditions, this may causedeformations on the order of several microns in the dimple shape, whichmay adversely impact the flight performance, and the appearance of thegolf ball may worsen due to solvent infiltration to the cover materialinterface that arises during molding.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a golf ball havinga scuff resistance, spin properties, ball appearance and the like thatare even better than those of prior-art golf balls.

The inventors have conducted extensive investigations, as a result ofwhich, in the earlier filed U.S. patent application Ser. No. 14/729,207,they disclosed a method of manufacturing a golf ball having a core and acover of one or more layer molded over the core, which method includesthe steps of: molding an outermost layer of the cover using athermoplastic material selected from the group consisting ofpolyurethane, polyurea and mixtures thereof; and subsequently treating asurface of the cover with a polyisocyanate compound that is free oforganic solvent. However, in this already disclosed invention, there isstill much room for improvement with regard to the support pin marksthat remain due to swelling after surface treatment of theinjection-molded cover.

The inventors have subsequently made further and repeated improvementsin this disclosed golf ball manufacturing method, as a result of whichthey have found that by blasting a substance such as water, alcohol, dryice, air or various types of abrasives at high pressure against theoutermost cover layer that has been treated with such an isocyanatecompound and thereby physically washing off and removing excessisocyanate compound present on the outermost cover layer, the resultingmanufactured ball has an excellent scuff resistance, maintains a lowspin rate on driver (W#1) shots, thus having a good flight performance,and has an unblemished appearance with no remaining pin marks frominjection molding in a mold.

Accordingly, the invention provides the following golf ball.

[1]A method of manufacturing a golf ball having a core and a cover ofone or more layer over the core, wherein an outermost layer of the coveris molded of a thermoplastic material selected from the group consistingof polyurethane, polyurea and mixtures thereof, the method including atleast the following steps (1) and (2):

(1) treating a surface of the cover with an isocyanate compound; and

(2) washing off and physically removing excess isocyanate compound byblasting the cover surface with a specific substance at high pressure.

[2] The golf ball manufacturing method of [1] wherein, in step (2), thespecific substance that is blasted at high pressure is at least oneselected from the group consisting of water, alcohol, dry ice, air,sand, vitrified abrasives, plastic abrasives, alumina abrasives, organicabrasives, metal abrasives, and mixtures thereof.[3] The golf ball manufacturing method of [1] wherein, in step (2),blasting with the specific substance is carried out at a dischargepressure of at least 3 MPa.[4] The golf ball manufacturing method of [1] wherein, in step (2),blasting with the specific substance is carried out at a temperature ofat least 5° C.[5] The golf ball manufacturing method of [1] wherein, in step (2),washing is carried out for a washing time of at least 10 seconds.[6] The golf ball manufacturing method of [1] wherein, when an infraredabsorption spectrum measured by FT-IR/ATR spectroscopy at an outsideportion of the outermost cover layer of the golf ball manufactured bysteps (1) and (2) is plotted as absorbance versus wave number, lettingthe absorbance peak heights near the wave numbers 1512 cm⁻¹, 2280 cm⁻¹and 2840 cm⁻¹ be respectively P₁, Q₁ and R₁, the value Q₁/R₁ is largerthan P₁.[7] The golf ball manufacturing method of [6], wherein the value Q₁/R₁is at least 0.3.[8] The golf ball manufacturing method of [6], wherein the value Q₁/R₁is at least 0.4.[9] The golf ball manufacturing method of [1], wherein the isocyanatecompound is one or a mixture of two or more selected from the groupconsisting of tolylene-2,6-diisocyanate, tolyene-2,4-diisocyanate,4,4′-diphenylmethanediisocyanate, polymethylene polyphenylpolyisocyanate, 1,5-diisocyanatonaphthalene, isophorone diisocyanate(including isomer mixtures), dicyclohexylmethane-4,4′-diisocyanate,hexamethylene-1,6-diisocyanate, m-xylylene diisocyanate, hydrogenatedxylylene diisocyanate, tolidine diisocyanate, norbornene diisocyanate,derivatives thereof, and prepolymers formed of said isocyanatecompounds.[10] The golf ball manufacturing method of [1] wherein, in step (10),the isocyanate compound is polymethylene polyphenyl polyisocyanate(polymeric MDI).

BRIEF DESCRIPTION OF THE DIAGRAMS

FIG. 1 shows an example of an infrared absorption spectrum (absorbanceversus wave number) measured by FT-IR/ATR spectroscopy at a specificportion of the outermost layer of a golf ball cover.

FIG. 2 is an enlarged view of part of the infrared absorption spectrumshown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described more fully below.

The inventive manufacturing method is a method of manufacturing golfballs by molding a cover of one or more layer over a core, in whichmethod an outermost layer of the cover is molded of a thermoplasticmaterial selected from the group consisting of polyurethane, polyureaand mixtures thereof.

In this invention, of the various cover layers, the outermost layer is alayer molded of a thermoplastic material selected from the groupconsisting of polyurethane, polyurea and mixtures thereof. Theproportion of the overall cover resin composition accounted for bypolyurethane, polyurea or a mixture thereof, although not particularlylimited, may be set to 50 wt % or more, and preferably 80 wt % or more.The polyurethane and polyurea are described below.

Polyurethane

The thermoplastic polyurethane material has a structure which includessoft segments composed of a polymeric polyol that is a long-chain polyol(polymeric glycol), and hard segments composed of a chain extender and apolyisocyanate. Here, the polymeric polyol serving as a startingmaterial is not subject to any particular limitation, and may be anythat is used in the prior art relating to thermoplastic polyurethanematerials. Exemplary polymeric polyols include polyester polyols,polyether polyols, polycarbonate polyols, polyester polycarbonatepolyols, polyolefin polyols, conjugated diene polymer-based polyols,castor oil-based polyols, silicone-based polyols and vinyl polymer-basedpolyols. Illustrative examples of polyester polyols includeadipate-based polyols such as polyethylene adipate glycol, polypropyleneadipate glycol, polybutadiene adipate glycol and polyhexamethyleneadipate glycol; and lactone-based polyols such as polycaprolactonepolyol. Illustrative examples of polyether polyols include poly(ethyleneglycol), poly(propylene glycol), poly(tetramethylene glycol) andpoly(methyltetramethylene glycol). These may be used singly or as acombination of two or more thereof.

The number-average molecular weight of these long-chain polyols ispreferably in the range of 500 to 5,000. By using a long-chain polyolhaving such a number-average molecular weight, golf balls made with athermoplastic polyurethane composition having excellent properties suchas the above-mentioned resilience and productivity can be reliablyobtained. The number-average molecular weight of the long-chain polyolis more preferably in the range of 1,500 to 4,000, and even morepreferably in the range of 1,700 to 3,500.

Here, and below, “number-average molecular weight” refers to thenumber-average molecular weight calculated based on the hydroxyl numbermeasured in accordance with JIS K-1557.

The chain extender is not particularly limited, although preferred usemay be made of those employed in the prior art relating to thermoplasticpolyurethanes. A low-molecular-weight compound which has a molecularweight of 2,000 or less and bears on the molecule two or more activehydrogen atoms capable of reacting with isocyanate groups may be used inthis invention, with the use of an aliphatic diol having from 2 to 12carbons being preferred. Specific examples of the chain extender include1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanedioland 2,2-dimethyl-1,3-propanediol. Of these, the use of 1,4-butyleneglycol is especially preferred.

The polyisocyanate compound is not subject to any particular limitation,although preferred use may be made of those employed in the prior artrelating to thermoplastic polyurethanes. Specific examples include one,two or more selected from the group consisting of 4,4′-diphenylmethanediisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate,p-phenylene diisocyanate, xylylene diisocyanate,naphthylene-1,5-diisocyanate, tetramethylxylene diisocyanate,hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate,tetramethylene diisocyanate, hexamethylene diisocyanate, isophoronediisocyanate, norbornene diisocyanate, trimethylhexamethylenediisocyanate, 1,4-bis(isocyanatomethyl)cyclohexane and dimer aciddiisocyanate. Depending on the type of isocyanate used, the crosslinkingreaction during injection molding may be difficult to control.

Although not an essential ingredient, a thermoplastic resin or elastomerother than a thermoplastic polyurethane may also be included. Morespecifically, use may be made of one, two or more selected from amongpolyester elastomers, polyamide elastomers, ionomer resins, styreneblock elastomers, hydrogenated styrene-butadiene rubbers,styrene-ethylene/butylene-ethylene block copolymers and modified formsthereof, ethylene-ethylene/butylene-ethylene block copolymers andmodified forms thereof, styrene-ethylene/butylene-styrene blockcopolymers and modified forms thereof, ABS resins, polyacetals,polyethylenes and nylon resins. The use of polyester elastomers,polyamide elastomers and polyacetals is especially preferred becausethese increase the resilience and scuff resistance due to reaction withthe isocyanate groups while yet maintaining a good productivity. Whenthese ingredients are included, the content thereof is suitably selectedso as to, for example, adjust the cover material hardness, improve theresilience, improve the flow properties or improve adhesion. The contentof these ingredients, although not particularly limited, may be set topreferably at least 5 parts by weight per 100 parts by weight of thethermoplastic polyurethane component. Although there is no particularupper limit, the content per 100 parts by weight of the thermoplasticpolyurethane component may be set to preferably not more than 100 partsby weight, more preferably not more than 75 parts by weight, and evenmore preferably not more than 50 parts by weight.

The ratio of active hydrogen atoms to isocyanate groups in the abovepolyurethane-forming reaction may be adjusted within a desirable rangeso as to make it possible to obtain golf balls which are made with athermoplastic polyurethane composition and have various improvedproperties, such as rebound, spin performance, scuff resistance andproductivity. Specifically, in preparing a thermoplastic polyurethane byreacting the above long-chain polyol, polyisocyanate compound and chainextender, it is desirable to use the respective components inproportions such that the amount of isocyanate groups included in thepolyisocyanate compound per mole of active hydrogen atoms on thelong-chain polyol and the chain extender is from 0.95 to 1.05 moles.

No particular limitation is imposed on the method of preparing thethermoplastic polyurethane. Preparation may be carried out by either aprepolymer process or a one-shot process using a known urethane-formingreaction.

A commercial product may be used as the above thermoplastic polyurethanematerial. Illustrative examples include the products available under thetrade name “Pandex” from DIC Bayer Polymer, Ltd., and the productsavailable under the trade name “Resamine” from Dainichiseika Color &Chemicals Mfg. Co., Ltd.

Polyurea

The polyurea is a resin composition composed primarily of urea linkagesformed by reacting (i) an isocyanate with (ii) an amine-terminatedcompound. This resin composition is described in detail below.

(i) Isocyanate

The isocyanate is preferably one that is used in the prior art relatingto thermoplastic polyurethanes, but is not subject to any particularlimitation. Use may be made of isocyanates similar to those describedabove in connection with the polyurethane material.

(ii) Amine-Terminated Compound

An amine-terminated compound is a compound having an amino group at theend of the molecular chain. In the present invention, the long-chainpolyamines and/or amine curing agents shown below may be used.

A long-chain polyamine is an amine compound which has on the molecule atleast two amino groups capable of reacting with isocyanate groups, andwhich has a number-average molecular weight of from 1,000 to 5,000. Inthis invention, the number-average molecular weight is more preferablyfrom 1,500 to 4,000, and even more preferably from 1,900 to 3,000.Within this average molecular weight range, an even better resilienceand productivity are obtained. Examples of such long-chain polyaminesinclude, but are not limited to, amine-terminated hydrocarbons,amine-terminated polyethers, amine-terminated polyesters,amine-terminated polycarbonates, amine-terminated polycaprolactones, andmixtures thereof. These long-chain polyamines may be used singly, or ascombinations of two or more thereof.

An amine curing agent is an amine compound which has on the molecule atleast two amino groups capable of reacting with isocyanate groups, andwhich has a number-average molecular weight of less than 1,000. In thisinvention, the number-average molecular weight is more preferably lessthan 800, and even more preferably less than 600. Such amine curingagents include, but are not limited to, ethylenediamine,hexamethylenediamine, 1-methyl-2,6-cyclohexyldiamine,tetrahydroxypropylene ethylenediamine, 2,2,4- and2,4,4-trimethyl-1,6-hexanediamine,4,4′-bis(sec-butylamino)dicyclohexylmethane,1,4-bis(sec-butylamino)cyclohexane, 1,2-bis(sec-butylamino)cyclohexane,derivatives of 4,4′-bis(sec-butylamino)dicyclohexylmethane,4,4′-dicyclohexylmethanediamine, 1,4-cyclohexane bis(methylamine),1,3-cyclohexane bis(methylamine), diethylene glycoldi(aminopropyl)ether, 2-methylpentamethylenediamine, diaminocyclohexane,diethylenetriamine, triethylenetetramine, tetraethylenepentamine,propylenediamine, 1,3-diaminopropane, dimethylaminopropylamine,diethylaminopropylamine, dipropylenetriamine, imido-bis(propylamine),monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine,diisopropanolamine, isophoronediamine,4,4′-methylenebis(2-chloroaniline), 3,5-dimethylthio-2,4-toluenediamine,3,5-dimethylthio-2,6-toluenediamine, 3,5-diethylthio-2,4-toluenediamine,3,5-diethylthio-2,6-toluenediamine,4,4′-bis(sec-butylamino)diphenylmethane and derivatives thereof,1,4-bis(sec-butylamino)benzene, 1,2-bis(sec-butylamino)benzene,N,N′-dialkylamino-diphenylmethane,N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine, trimethylene glycoldi-p-aminobenzoate, polytetramethylene oxide di-p-aminobenzoate,4,4′-methylenebis(3-chloro-2,6-diethyleneaniline),4,4′-methylenebis(2,6-diethylaniline), m-phenylenediamine,p-phenylenediamine and mixtures thereof. These amine curing agents maybe used singly or as combinations of two or more thereof.

(iii) Polyol

Although not an essential component, in addition to the above-describedcomponents (i) and (ii), a polyol may also be included in the polyurea.In this invention, the polyol is not particularly limited, but ispreferably one that has hitherto been used in the art relating tothermoplastic polyurethanes. Specific examples include the long-chainpolyols and/or polyol curing agents described below.

The long-chain polyol may be any that has hitherto been used in the artrelating to thermoplastic polyurethanes. Examples include, but are notlimited to, polyester polyols, polyether polyols, polycarbonate polyols,polyester polycarbonate polyols, polyolefin-based polyols, conjugateddiene polymer-based polyols, castor oil-based polyols, silicone-basedpolyols and vinyl polymer-based polyols. These long-chain polyols may beused singly or as combinations of two or more thereof.

The long-chain polyol has a number-average molecular weight ofpreferably from 500 to 5,000, and more preferably from 1,700 to 3,500.In this average molecular weight range, an even better resilience andproductivity are obtained.

The polyol curing agent is preferably one that has hitherto been used inthe art relating to thermoplastic polyurethanes, but is not subject toany particular limitation. In this invention, use may be made of alow-molecular-weight compound having on the molecule at least two activehydrogen atoms capable of reacting with isocyanate groups, and having amolecular weight of less than 1,000. Of these, the use of aliphaticdiols having from 2 to 12 carbons is preferred. Specific examplesinclude 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol,1,6-hexanediol and 2,2-dimethyl-1,3-propanediol. The use of 1,4-butyleneglycol is especially preferred. The polyol curing agent has anumber-average molecular weight of preferably less than 800, and morepreferably less than 600.

Where necessary, various additives may also be included in thepolyurethane and polyurea. For example, pigments, inorganic fillers,dispersants, antioxidants, light stabilizers, ultraviolet absorbers andmold release agents may be suitably included.

A known method may be used to produce the polyurea. A prepolymerprocess, a one-shot process or some other known method may be suitablyselected for this purpose.

The method of molding the cover using the polyurethane and the polyureamay involve, for example, feeding these materials to aninjection-molding machine and injecting them over the core. The moldingtemperature in such a case varies depending on the formulation and otherfactors, but is generally in the range of 150 to 270° C.

Step (1): Treatment with Isocyanate Compound

The inventive manufacturing method includes a step in which the surfaceof the outermost cover layer molded as described above is treated withan isocyanate compound. This treatment method is described below.

The treatment method uses an isocyanate compound, with the use of anisocyanate compound containing no organic solvent being preferred. Here,the isocyanate compound, although not particularly limited, is typicallyselected from the following group.

<Group of Isocyanate Compounds for Selection>

The group consisting of tolylene-2,6-diisocyanate,tolylene-2,4-diisocyanate, 4,4′-diphenylmethane diisocyanate,polymethylene polyphenyl polyisocyanate, 1,5-diisocyanatonaphthalene,isophorone diisocyanate (including isomer mixtures),dicyclohexylmethane-4,4′-diisocyanate, hexamethylene-1,6-diisocyanate,m-xylylene diisocyanate, hydrogenated xylylene diisocyanate, tolidinediisocyanate, norbornene diisocyanate, derivatives of these, andprepolymers formed of such isocyanate compounds.

An aromatic isocyanate compound is preferably used as the isocyanatecompound, with the use of 4,4′-diphenylmethane diisocyanate (monomeric,or “pure,” MDI) or polymethylene polyphenyl polyisocyanate (polymericMDI) being especially preferred. When an aromatic isocyanate compound isused in the invention, because it has a high reactivity with thereactive groups on the thermoplastic resin, the intended effects of theinvention can be successfully achieved. The use of polymeric MDI ispreferred because it has a larger number of isocyanate groups thanmonomeric MDI and thus provides a large scuff resistance-improvingeffect due to crosslink formation, and moreover because it is in aliquid state at normal temperatures and thus has an excellenthandleability. However, polymeric MDI generally has a dark brownappearance, which may discolor and contaminate the cover material to betreated. Because such discoloration is pronounced when treatment iscarried out with polymeric MDI in the form of a solution obtained bydissolution in an organic solvent, in the practice of the invention,owing to concern over such discoloration, the polymeric MDI is used in astate that is free of organic solvents. Alternatively, commercialproducts may be suitably used as the polymeric MDI. Illustrativeexamples include Sumidur p-MDI 44V20L, 44V10, 44V40 and SBU IsocyanateJ243 from Sumika Bayer Urethane Co., Ltd.; MONDUR MR Light from BayerMaterial Science; PAPI 27 from Dow Chemical Company; Millionate MR-100,MR-200 and MR-400 from Tosoh Corporation; and Lupranate M20S, M11S andM5S from BASF INOAC Polyurethane, Ltd.

In this invention, the preliminary treatments described in, for example,JP 4114198 and JP 4247735 may be suitably used as methods for reducingdiscoloration by polymeric MDI. Although the techniques described inthese patent publications may be adopted for use here, the possibilitiesare not limited to these techniques alone. When such preliminarytreatment is carried out and the treatment is followed by suitablewashing, substantially no discoloration or contamination arises.

A dipping method, coating method (spraying method), infiltration methodunder heat and pressure application, dropwise addition method or thelike may be suitably used as the method of treating the surface with theisocyanate compound. From the standpoint of process control andproductivity, the use of a dipping method, coating method or dropwiseaddition method is especially preferred. The length of treatment by thedipping method is preferably from 1 to 180 minutes, more preferably from10 to 120 minutes, and even more preferably from 20 to 90 minutes. Whenthe treatment time is too short, a sufficient crosslinking effect isdifficult to obtain. On the other hand, when the treatment time is toolong, there is a possibility of substantial discoloration of the coversurface by excess isocyanate compound. Also, with a long treatment time,the production lead time becomes long, which is not very desirable fromthe standpoint of productivity. With regard to the temperature duringsuch treatment, from the standpoint of productivity, it is preferable tocontrol the temperature within a range that allows a stable moltenliquid state to be maintained and also allows the reactivity to bestably maintained. The temperature is preferably from 10 to 80° C., morepreferably from 15 to 70° C., and even more preferably from 20 to 60° C.When the treatment temperature is too low, infiltration and diffusion tothe cover material or reactivity at the surface layer interface may beinadequate, as a result of which the desired properties may not beachieved. On the other hand, when the treatment temperature is too high,infiltration and diffusion to the cover material or reactivity at thesurface layer interface may increase and there is a possibility ofgreater discoloration of the cover surface on account of excessisocyanate compound. Also, in cases where the ball appearance—includingthe shapes of the dimples—changes, or an ionomeric material is used inpart of the golf ball, there is a possibility that this will give riseto changes in the physical properties of the ball. By carrying outtreatment for a length of time and at a temperature in these preferredranges, it is possible to obtain a sufficient crosslinking effect and,in turn, to achieve the desired ball properties without a loss ofproductivity.

To control the reactivity and obtain a golf ball having an even betterscuff resistance and spin performance, a catalyst or a compound havingtwo, three or more functional groups that react with isocyanate groupscan be incorporated beforehand in the isocyanate compound treatmentagent or in the cover material to be treated. The method ofincorporating such a compound may involve mixing the compound, in adispersed state, with a liquid melt of the isocyanate compound treatmentagent; using a mixer such as a single-screw or twin-screw extruder tomix the compound into the thermoplastic resin that is the material to betreated (cover material); or charging the respective ingredients in adry blended state into an injection molding machine. When the last ofthese methods is used, during charging, the compound may be chargedalone, or may be rendered beforehand into a masterbatch state using asuitable base material.

Drying treatment may be carried out preliminary to surface treatmentwith the above isocyanate compound. That is, when treating the covermolded from a thermoplastic material that includes a polyurethane, apolyurea or a mixture thereof, to remove moisture contained in the covermaterial and thereby stabilize the physical properties followingtreatment and increase the life of the treatment solution, it may bedesirable to carry out, as needed, drying treatment or the likebeforehand, although this is not always the case. A common method suchas warm-air drying or vacuum drying may be used as the drying treatment.Such treatment preliminary to surface treatment, particularly in thecase of golf balls containing an ionomeric material in a portionthereof, is preferably carried out under conditions that do not causedeformation or changes in the physical properties. When warm air dryingis carried in such preliminary treatment, although not particularlylimited, it is desirable to set the temperature to from 15 to 60° C.,and preferably from 20 to 55° C., and to set the time to preferably from10 to 180 minutes, more preferably from 15 to 120 minutes, and even morepreferably from 30 to 60 minutes. The drying conditions may be suitablyselected according to the moisture content within the cover material andare typically adjusted so that the moisture content in the covermaterial becomes preferably 5,000 ppm or less, more preferably 3,500 ppmor less, even more preferably 2,500 ppm or less, and most preferably1,000 ppm or less.

Step (2): Washing

Next, excess isocyanate compound is washed off and physically removed byblasting a specific substance at high pressure against the surface ofthe cover. This step removes excess isocyanate compound remaining on theoutermost cover layer following surface treatment with isocyanatecompound but does not completely remove from all areas of the outermostcover layer the isocyanate compound that has impregnated into and ispresent within this layer, thus allowing the advantageous effects ofsurface treatment with the isocyanate compound in the preceding step tobe fully exhibited. That is, the scuff resistance of the ball can beincreased and the spin rate on driver (W#1) shots is sufficientlyreduced, making it possible to achieve a satisfactory distance.

In the washing step, the specific substance that is blasted at highpressure is not particularly limited. However, preferred use can be madeof at least one type of substance selected from the group consisting ofsubstances that are liquids at normal temperatures, such as water andalcohol; substances that are solids, such as sand, vitrified abrasives,plastic abrasives, alumina abrasives, organic abrasives and metalabrasives; normally gaseous substances such as air and substances suchas dry ice which sublimate from a solid state to a gaseous state atnormal temperatures; as well as mixtures thereof.

In this washing step, the discharge pressure when blasting the specificsubstance is set to a high pressure. Specifically, the dischargepressure is preferably at least 3 MPa, more preferably at least 6 MPa,and even more preferably at least 8 MPa.

The use of water or an alcohol as the specific substance to be blastedis preferred because the amount of isocyanate (NCO groups) which remainswithout being excessively removed increases, and it is possible to lowerthe temperature of surface treatment with isocyanate compound or toshorten the treatment time. Also, as will be explained later in thespecification, whereas contact with water or alcohol is normally bannedfor isocyanate compounds, the significance of the invention resides inthe intentional use of water or alcohol. When such water or alcohol isused, the discharge rate by a high-pressure washer is preferably atleast 180 L/h, more preferably at least 300 L/h, and even morepreferably at least 400 L/h.

In this washing step, the temperature when blasting the specificsubstance, although not particularly limited, is preferably at least 5°C., more preferably from 10° C. to 80° C., and even more preferably from15° C. to 60° C. The washing time, although not particularly limited, ispreferably at least 10 seconds, and more preferably from 15 to 30seconds.

Exemplary high-pressure washers include commercial high-pressure washerssuch as those manufactured by, for example, Karcher, Ryobi, Iris Ohyama,Hidaka or Hitachi.

In this invention, employing this washing step has the following actionsand desirable effects.

(i) When washing with an organic solvent that dissolves the isocyanatecompound and has no reactive groups capable of reacting with theisocyanate compound, there is a possibility that the solvent will causethe polyurethane in the outermost cover layer to swell, and there isalso a possibility that even isocyanate compound that has impregnated tothe interior will be removed. Water and alcohols have reactive groupsthat react with isocyanate, leading to reaction and solidification,which is why contact with water and alcohol was strictly banned.

However, in this invention, because the isocyanate compound is notexcessively removed, the scuff resistance can be improved, in additionto which the spin rate on shots with a driver (W#1) can be adequatelyreduced.

(ii) The above washing step does not require, for example, numerousoperations or a large amount of material, and thus can be carried outrelatively inexpensively, resulting in economical reductions in costssuch as material costs and equipment costs.(iii) Rather than using organic solvents which cause the polyurethane toswell, dissolve the isocyanate compound and have no reactive groupscapable of reacting with the isocyanate compound, the above washing stepuses water or a relatively safe alcohol, and thus is friendly to theenvironment.(iv) Isocyanate compounds readily react with water or alcohol andsolidify and at the same time generate carbon dioxide, and so contactwith water and alcohols is generally banned. However, in the inventivemanufacturing method, with high-pressure washing, the isocyanatecompound becomes finely dispersed within a large amount of washingsolution, allowing it to be relatively safely used. Moreover, becausewater and alcohols render the isocyanate compound into a solidifiedstate within the wash solution after washing, this solid matter can beeasily removed, enabling the wash solution to be reused.(v) When washing is carried out with an organic solvent that causes thepolyurethane to swell after surface treatment, dissolves the isocyanatecompound and has no reactive groups capable of reacting with theisocyanate compound, one problem has been the swelling of pin marks thatare formed by the plurality of support pins used in injection moldingand remain on the molded ball. Because the washing step in thisinvention does not involve washing with an organic solvent that causesthe polyurethane to swell after surface treatment, dissolves theisocyanate compound and has no reactive groups capable of reacting withthe isocyanate compound, pin marks due to support pins do not remain onthe molded ball, enabling a good ball appearance to be maintained.

Following surface treatment with the isocyanate compound, it ispreferable to provide a suitable curing step in order to have thecrosslinking reactions between the polyurethane or polyureathermoplastic material and the isocyanate compound effectively proceed,thereby enhancing and stabilizing the physical properties and quality,and also to control and shorten the production takt time. However,because reaction of the isocyanate proceeds even at room temperature, itis not always necessary to provide a curing step. In cases where acuring step is provided, a method that causes the crosslinking reactionsto proceed under the effect of heat or pressure and in the presence of acatalyst may be suitably selected. Specifically, it is preferable tocarry out heating treatment under suitable temperature and timeconditions that are typically from 15 to 150° C. for up to 24 hours,preferably from 20 to 100° C. for up to 12 hours, and more preferablyfrom 30 to 70° C. for up to 6 hours.

The degree to which, following surface treatment with the isocyanatecompound, crosslinking reactions between the polyurethane or polyureathermoplastic material and the isocyanate compound have proceeded can bedetermined by a suitable technique. For example, it is effective to useattenuated total reflectance (ATR) Fourier transform infrared absorptionspectroscopy (FT-IR) to measure the ball surface after curing.

Specifically, when an infrared absorption spectrum measured by FT-IR/ATRspectroscopy at an outside portion of the outermost cover layer of thegolf ball manufactured by steps (1) and (2) is plotted as absorbanceversus wave number, letting the absorbance peak heights near the wavenumbers 1512 cm⁻¹, 2280 cm⁻¹ and 2840 cm⁻¹ be respectively P₁, Q₁ andR₁, the value Q₁/R₁ is preferably larger than P₁. The absorbance peakheight P₁ near the wave number 1512 cm⁻¹ is the absorbance peak heightfor bending vibrations by the amide groups (NHCO groups) in urethanebonds. The absorbance peak height near the wave number 2280 cm⁻¹represents the peak intensity from isocyanate groups (NCO groups), andthe absorbance peak height near the wave number 2840 cm¹ represents thepeak intensity from CH stretching vibrations. Hence, the foregoingrelationship indicates that the peak intensity from isocyanate groups(NCO groups) is somewhat high. Compared to washing with an organicsolvent such as acetone, the washing method used in this inventionleaves many isocyanate groups (NCO groups) within the outermost coverlayer, enabling ball attributes such as scuff resistance and spinproperties to be improved.

Here, FIG. 1 shows the infrared absorption spectrum measured byFT-IR/ATR spectroscopy and represented as a plot of absorbance versuswave number, and FIG. 2 is an enlarged view of part of the spectrumshown in FIG. 1. As shown in FIG. 2, baseline correction is carried outso as to set the absorbances at wave numbers of 1494 cm⁻¹ and 1571 cm⁻¹to 0, and P₁ is determined as the absorbance peak height followingcorrection. The absorbance peak height is computed relative to abaseline in order to correct for the variability in the measured valuesfor absorbance that arises with each measurement. To increase theaccuracy of the measured data, the absorbance peak height is determinedby increasing the number of measurements (N) so as to have the relativestandard deviation (%) (also referred to below as “RSD”) be 3.0% orless. The relative standard deviation (%) is expressed by the followingformula.

Relative standard deviation (%)=(standard deviation/average value)×100

The value Q₁/R₁ is preferably at least 0.3, and more preferably at least0.4. Outside of this range, the scuff resistance is inferior and a good,low spin rate on shots with a driver (W#1) may not be obtained.

FT-IR analysis at the outside portion of the outermost cover layerentails measurement by the ATR method or by the ATR method with IRmicroscopy after preparation of an unpainted ball, or, when a paintedball is to be used, after removing the paint, so that the sample surfaceis sufficiently smooth. As used herein, “outside portion of theoutermost layer” refers to a portion that includes not only a surface ofthe outermost layer, but also extends up to a region 100 μm from thissurface and toward the core center. In carrying out measurement, thenumber of measurements (N) is increased until the relative standarddeviation of the measurement data becomes 3.0% or less. Because it takesseveral days for progress of the crosslinking reactions to stabilize, itis preferable to measure the samples when about one week has elapsedfollowing treatment. FT-IR/ATR spectroscopy may be carried out inaccordance with the method described in JIS K 0117.

The method of molding the outermost layer of the cover is exemplified bya method that feeds the resin composition to an injection moldingmachine and injects the molten resin composition over the core, therebymolding the outermost layer of the cover. In such cases, the moldingtemperature varies according to such factors as the type ofthermoplastic polyurethane, but is generally in the range of 150 to 270°C.

In the cover of one or more layer forming a part of the inventive golfball, the ball surface hardness following the above-described surfacetreatment, expressed in terms of Durometer D hardness, is preferablyfrom 30 to 70, and more preferably from 33 to 65. When the hardness ofthe outermost cover layer is too low, the spin rate of the ball on shotswith a driver may rise, resulting in a decreased distance. On the otherhand, when the hardness of the cover outermost layer is too high, thefeel at impact may worsen and the resulting rebound and durabilityperformance may be inferior to those of the urethane material itself.

The rebound resilience of the outermost layer prior to the above surfacetreatment, although not particularly limited, is preferably at least35%, more preferably at least 40%, and even more preferably at least45%. If the rebound resilience of the cover outermost layer is too low,the distance traveled by the golf ball may greatly decrease. On theother hand, if the rebound resilience of the outermost layer of thecover is too high, the initial velocity on shots of up to 100 yards thatrequire control and on putts becomes too high and may not feel right tothe golfer. As used herein, “rebound resilience” refers to the reboundresilience measured in accordance with JIS K7311.

The core used in the golf ball of the invention is not particularlylimited. Use may be made of various types of cores, such as, forexample, a solid core for a two-piece ball, a solid core having aplurality of vulcanized rubber layers, a solid core having a pluralityof resin layers, or a wound core having a layer of rubber thread. Nolimitations are imposed on the diameter, weight, hardness, constituentmaterials and other characteristics of the core.

In the golf ball of the invention, when the cover has two or morelayers—that is, when the cover has a construction which includes anintermediate layer to the inside of the outermost layer, no particularlimitations are imposed on the hardness, material, thickness and othercharacteristics of the intermediate layer. To improve adherence betweenthe intermediate layer and the outermost layer, where necessary, aprimer layer may be provided or a common known technique for improvingadherence or adhesion may be employed. Examples of common knowntechniques include plasma surface treatment (e.g., microwave plasmatreatment, high-frequency plasma treatment, atmospheric pressure plasmatreatment), corona discharge treatment, flame treatment, treatment byexposure to ultraviolet irradiation, chlorine treatment, treatment bywiping the surface with an organic solvent, silane coupling agentcoating treatment, honing treatment, chemical etching treatment andphysical surface roughening treatment. These types of treatment may beused singly or as combinations of two or more thereof.

The thickness of the outermost layer of the cover may be set in therange of 0.1 to 5.0 mm, preferably 0.3 to 3.0 mm, and more preferably0.5 to 2.0 mm. In cases where the cover is formed so as to have amultilayer structure of two or more layers, the thickness of theintermediate layer, although not particularly limited, may be set in therange of 0.1 to 5.0 mm, preferably 0.3 to 3.0 mm, and more preferably0.5 to 2.0 mm.

The golf ball of the invention is preferably formed to a diameter andweight in accordance with the Rules of Golf.

Examples

Working Examples of the invention and Comparative Examples are givenbelow by way of illustration, although the invention is not limited bythe following Examples.

Examples 1 to 12, Comparative Examples 1 to 6

Cores having a diameter of 36.3 mm were produced by using theformulation shown in Table 1 to prepare a core-forming rubbercomposition common to all the Examples, then curing and molding at 155°C. for 15 minutes. Next, cover layers (these being, in order from theinside: an envelope layer and an intermediate layer) formulated of theresin materials shown in the same table and common to all the Exampleswere successively injection-molded over the core, thereby giving anintermediate sphere. The envelope layer had a thickness of 1.3 mm and amaterial hardness, expressed in terms of Shore D hardness, of 51. Theintermediate layer had a thickness of 1.1 mm and a material hardness,expressed in terms of Shore D hardness, of 62.

The outermost cover layer, which is common to all the Examples, wasinjection-molded over the intermediate sphere so as to encase thesphere. The resin materials used to form the outermost layer are shownin Table 2. The outermost layer had a thickness of 0.8 mm. Although notshown in the accompanying diagrams, numerous dimples were formed on theoutside surface of the outermost layer at the same time as injectionmolding.

TABLE 1 Ball component Formulated ingredients Amounts Cover Intermediatelayer Himilan 1605 50 Himilan 1557 15 Himilan 1706 35 Trimethylolpropane1.1 Envelope layer HPF1000 100 Core Polybutadiene A 80 Polybutadiene B20 Organic peroxide 1 Barium sulfate 21.5 Zinc oxide 4 Zinc acrylate29.5 Antioxidant 0.1 Zinc salt of 0.3 pentachlorothiophenol

Details on these core materials are given below. Numbers in the tableindicate parts by weight.

-   Polybutadiene A: Available from JSR Corporation under the trade name    “BR 01”-   Polybutadiene B: Available from JSR Corporation under the trade name    “BR 51”-   Organic Peroxide: Dicumyl peroxide, available under the trade name    “Percumyl D” (NOF Corporation)-   Barium sulfate: Available from Sakai Chemical Co., Ltd. as    “Precipitated Barium Sulfate 100”-   Zinc oxide: Available from Sakai Chemical Co., Ltd.-   Zinc acrylate: Available from Nihon Joryu Kogyo Co., Ltd.-   Antioxidant: 2,2′-Methylenebis(4-methyl-6-butylphenol), available    under the trade name “Nocrac NS-6” (Ouchi Shinko Chemical Industry    Co., Ltd.)

Details on the cover (envelope layer, intermediate layer) materials aregiven below. Numbers in the table indicate parts by weight.

-   HPF 1000: An ionomer from E.I. DuPont de Nemours & Co.-   Himilan 1605: A sodium ionomer from DuPont-Mitsui Polychemicals Co.,    Ltd.-   Himilan 1557: A zinc ionomer from DuPont-Mitsui Polychemicals Co.,    Ltd.-   Himilan 1706: A zinc ionomer from DuPont-Mitsui Polychemicals Co.,    Ltd.

TABLE 2 Resin formulation (pbw) II Pandex T8290 50 Pandex T8295 50Hytrel 4001 12 Titanium oxide 3.5 Ultramarine 0.4 Polyethylene wax 1Montan wax 0.4

Details on the cover (outermost layer) materials are given below.Numbers in the table indicate parts by weight.

-   T-8290, T-8295: Ether-type thermoplastic polyurethanes available    under the trademark Pandex from DIC Bayer Polymer-   Hytrel 4001: A polyester elastomer available from DuPont-Toray Co.,    Ltd.-   Polyethylene wax: Available under the trade name “Sanwax 161P” from    Sanyo Chemical Industries, Ltd.-   Titanium oxide: Tipaque R680, available from Ishihara Sangyo Kaisha,    Ltd.

Immersion Treatment

Next, in each of the Working Examples and Comparative Examples, surfacetreatment was carried out at the surface of the outermost layer usingpolymeric MDI available under the trade name “Sumidur p-MDI 44V20L” fromSumika Bayer Urethane Co., Ltd. This surface treatment involvedsuccessively carrying out the following steps: (i) 60 minutes ofpreliminary warming at 55° C., and (ii) dipping treatment in which theentire ball was thoroughly immersed in isocyanate compound alone withoutusing a solvent, under the temperature and time conditions shown inTables 3, 4 and 5.

Washing Treatment

Next, a step was carried out that consisted of washing off andphysically removing excess isocyanate compound by blasting the surfaceof the outermost layer in each Example at high pressure with thespecific substances (washing solutions) shown in Tables 3 and 4. Theconditions of the washing step in the respective Examples—namely, thewashing solution, washing method, discharge pressure, discharge rate,washing solution temperature and washing time—are shown in Tables 3 and4. A Karcher HD 4/8C pressure washer was used as the high-pressurewasher in the Examples. The washing step was carried out by placing thegolf balls that had been immersion treated with isocyanate compound in abasket made of metal mesh, setting up the high-pressure washer at adistance of about 20 cm from the balls, and washing the balls whilerotating the basket at a speed of 20 rpm. In the Comparative Examples,washing was carried out by dipping the surface of the outermost coverlayer in the organic solvents shown in Table 5 for 30 seconds at 15° C.

Curing Step

Following the above washing treatment, 60 minutes of curing was carriedout at 55° C.

Golf balls on which the above surface treatment, washing treatment andcuring step had been carried out were tested and evaluated by themethods described below. The results are shown in Tables 3, 4 and 5.

FTR Absorbance at Outside Portion of Outermost Layer

Samples were prepared by peeling the outermost cover layer from theintermediate layer. In order for the place of measurement on the coversurface to be in sufficiently close contact with the FT-IR measurementsurface, measurement was carried out after pressing the center portionof a dimple from the back side of the cover so as to bring it into closecontact with the measurement surface. When the infrared absorptionspectrum measured by FT-IR/ATR spectroscopy at an outside portion of theoutermost cover layer was plotted as absorbance versus wave number, theabsorbance peak heights near the wave numbers 1512 cm⁻¹, 2280 cm⁻¹ and2840 cm⁻¹ were designated as, respectively, P₁, Q₁ and R₁. To increasethe accuracy of the measurement data, each absorbance peak height wasdetermined by carrying out measurement N times so that the relativestandard deviation (%) (referred to below as “RSD %”) becomes 3.0% orless. Measurement was carried out seven days after surface treating theoutermost layer. The instrument used for FT-IR/ATR measurement was the“Spectrum 100, System B” Fourier-transform infrared spectrophotometer(from Perkin Elmer). Samples were measured under the followingconditions.

Measurement method: Attenuated total reflection (ATR)

Detector: FR-DTGS

Resolution: 4 cm⁻¹

Cumulative number: 16 times

Measurement wave number range: 4000 cm⁻¹ to 650 cm⁻¹

Place of measurement:

-   -   [Outside portion] Surface portion of dimple center

Scuff Resistance

The balls were held isothermally at 23° C. and five balls of each typewere hit at a head speed of 33 m/s using as the club a pitching wedgemounted on a swing robot machine. The damage to the ball from the impactwas visually evaluated based on the following 5-point scale, and theaverage score for each type of ball was calculated.

-   -   5: No damage or substantially no damage.    -   4: Damage is apparent but so slight as to be of substantially no        concern.    -   3: Surface is slightly frayed.    -   2: Some fraying of surface or loss of dimples.    -   1: Dimples completely obliterated in places.

Flight Performance

A driver (W#1) was mounted on a golf swing robot, and the spin rate andtotal distance when the ball was struck at a head speed of 45 m/s weremeasured. The club used was a TourStage X-Drive 707 (2012 model; loftangle, 9.5°) manufactured by Bridgestone Sports Co., Ltd.

Appearance (Completeness of Washing)

The appearance (surface) of the ball after washing was examined forremaining stains due to incomplete washing, and rated according to thefollowing criteria. Stains that remain on the surface of the ball maydetract from the ball appearance, worsen the weather resistance of theball, and also give rise to undesirable effects such as peeling of thepaint film when the ball is struck.

-   -   Good: No remaining stains due to incomplete washing.    -   Fair: Slight amount of remaining stains due to incomplete        washing.    -   NG: Substantial amount of remaining stains due to incomplete        washing.

Evaluation of Pin Marks (NG Ratio)

Pin marks on the ball surface were graded by the following method. Thepin areas of the ball surface were rubbed with a black oil-based coloredpencil and then wiped with a dry cloth. After wiping, the number of pinmarks where the black pencil remained in the pin areas was counted.Letting this number be “NG,” the NG ratio (%) with respect to the totalnumber of pins present on a single ball was calculated.

TABLE 3 Example 1 2 3 4 5 6 Immersion Treatment temperature (° C.) 53 5353 53 53 53 treatment Treatment time (min) 40 40 40 40 30 30 WashingWashing solution high- high- high- high- high- high- treatment pressurepressure pressure pressure pressure pressure water water water waterwater water Washing method high- high- high- high- high- high- pressurepressure pressure pressure pressure pressure blasting blasting blastingblasting blasting blasting Discharge pressure (MPa) 8 3 8 8 8 8Discharge rate (L/h) 400 180 400 400 400 400 Temperature of 15 15 15 155 10 washing solution (° C.) Washing time (sec) 10 30 20 30 30 30Outermost FT-IR P1 0.241 0.237 0.238 0.236 0.237 0.238 layer analysis Q10.082 0.084 0.077 0.070 0.081 0.078 R1 0.153 0.151 0.149 0.142 0.1500.148 Q1/R1 0.536 0.556 0.517 0.494 0.540 0.527 (Q1/R1) > P1 good goodgood good good good Q1/R1 ≧ 0.3 good good good good good good Q1/R1 ≧0.4 good good good good good good Ball Diameter (mm) 42.72 42.73 42.7042.68 42.69 42.67 performance Weight (g) 45.50 45.52 45.45 45.43 45.4545.47 Scuff resistance 4.9 4.9 4.7 4.5 4.8 4.7 (23° C. average) Spinrate rpm 2,952 2,950 2,960 2,964 2,950 2,965 on shots Difference with−155 −157 −147 −143 −157 −142 with driver Comparative Example 1 (rpm)Total distance (m) 229 229 229 229 229 230 Appearance Rating fair fairgood good fair good (completeness of washing) Pin mark NG ratio (%) 0 00 0 0 0

TABLE 4 Example 7 8 9 10 11 12 Immersion Treatment temperature (° C.) 5353 53 53 53 53 treatment Treatment time (min) 30 30 30 30 30 30 WashingWashing solution high- high- high- high- high- high- treatment pressurepressure pressure pressure pressure pressure water water water waterwater water Washing method high- high- high- high- high- high- pressurepressure pressure pressure pressure pressure blasting blasting blastingblasting blasting blasting Discharge pressure (MPa) 8 8 8 8 8 8Discharge rate (L/h) 400 400 400 400 400 400 Temperature of 15 30 60 6060 60 washing solution (° C.) Washing time (sec) 30 20 10 15 20 30Outermost FT-IR P1 0.234 0.234 0.237 0.234 0.239 0.241 layer analysis Q10.069 0.070 0.081 0.076 0.062 0.056 R1 0.140 0.141 0.151 0.148 0.1520.149 Q1/R1 0.493 0.496 0.536 0.514 0.408 0.376 (Q1/R1) > P1 good goodgood good good good Q1/R1 ≧ 0.3 good good good good good good Q1/R1 ≧0.4 good good good good good NG Ball Diameter (mm) 42.66 42.69 42.7142.69 42.67 42.65 performance Weight (g) 45.41 45.42 45.49 45.48 45.4645.44 Scuff resistance 4.5 4.5 4.8 4.6 4.4 4.3 (23° C. average) Spinrate rpm 2,979 2,970 2,963 2,968 2,979 2,998 on shots Difference with−128 −137 −144 −139 −128 −109 with driver Comparative Example 1 (rpm)Total distance (m) 229 230 230 228 229 229 Appearance Rating good goodfair good good good (completeness of washing) Pin mark NG ratio (%) 0 00 0 0 0

TABLE 5 Comparative Example 1 2 3 4 5 6 Immersion Treatment temperature(° C.) 53 53 53 53 53 53 treatment Treatment time (min) 40 40 40 40 4040 Washing Washing solution acetone ethyl toluene cyclo- MEK MIBKtreatment acetate hexanone Washing method dipping dipping dippingdipping dipping dipping Discharge pressure (MPa) — — — — — — Dischargerate (L/h) — — — — — — Temperature of 15 15 15 15 15 15 washing solution(° C.) Washing time (sec) 30 30 30 30 30 30 Outermost FT-IR P1 0.1940.199 0.198 0.202 0.199 0.206 layer analysis Q1 0.011 0.030 0.031 0.0150.013 0.019 R1 0.164 0.159 0.158 0.161 0.162 0.163 Q1/R1 0.064 0.1890.196 0.093 0.080 0.117 (Q1/R1) > P1 NG NG NG NG NG NG Q1/R1 ≧ 0.3 NG NGNG NG NG NG Q1/R1 ≧ 0.4 NG NG NG NG NG NG Ball Diameter (mm) 42.68 42.7042.69 42.67 42.68 42.71 performance Weight (g) 45.43 45.43 45.42 45.4845.44 45.52 Scuff resistance 3.9 4.0 4.0 3.9 4.0 4.0 (23° C. average)Spin rate rpm 3,107 3,046 3,063 3,085 3,073 3,062 on shots Differencewith — −61 −44 −22 −34 −45 with driver Comparative Example 1 (rpm) Totaldistance (m) 228 229 230 228 229 229 Appearance Rating good fair goodgood good fair (completeness of washing) Pin mark NG ratio (%) 81 92 8783 81 83 * In the table, “MEK” stands for methyl ethyl ketone, and“MIBK” stands for methyl isobutyl ketone.

The ball performance results in Tables 3 to 5 are discussed below.

Examples 1, 3 and 4 had better scuff resistances than ComparativeExamples 1 to 6, achieved satisfactory total distances on shots with adriver (W#1) owing to a reduced spin rate, and had an appearanceunblemished by pin marks.

Example 2 had a lower discharge pressure and discharge rate than inExample 4, a higher scuff resistance and a larger spin rate-loweringeffect. Relative to Comparative Examples 1 to 6, the scuff resistancewas excellent, a spin rate-lowering effect on shots with a driver (W#1)was obtained, resulting in a satisfactory total distance, and the ballhad an appearance unblemished by pin marks.

Although Example 7 had a shorter treatment time than in Example 4,relative to Comparative Examples 1 to 6, the scuff resistance wasexcellent, a spin rate-lowering effect on shots with a driver (W#1) wasobtained, resulting in a satisfactory total distance, and the ball hadan appearance unblemished by pin marks.

Examples 5 and 6 had a lower washing solution temperature than inExample 7, a higher scuff resistance and a larger spin rate-loweringeffect. Also, relative to Comparative Examples 1 to 6, the scuffresistance was excellent, a spin rate-lowering effect on shots with adriver (W#1) was obtained, resulting in a satisfactory total distance,and the ball had an appearance unblemished by pin marks.

Examples 8, 10 and 11 had a higher washing solution temperature and ashorter washing time than in Example 7, yet achieved a comparableperformance. Relative to Comparative Examples 1 to 6, the scuffresistance was excellent, a spin rate-lowering effect on shots with adriver (W#1) was obtained, resulting in a satisfactory total distance,and the ball had an appearance unblemished by pin marks.

Example 9 had an even shorter washing time, and a better scuffresistance and spin rate-lowering effect, than in Examples 10 and 11.Also, relative to Comparative Examples 1 to 6, the scuff resistance wasexcellent, a spin rate-lowering effect on shots with a driver (W#1) wasobtained, resulting in a satisfactory total distance, and the ball hadan appearance unblemished by pin marks.

Example 12 had a longer wash time than in Examples 9 to 11 and a scuffresistance and spin-rate lowering effect that were somewhat inferior.However, relative to Comparative Examples 1 to 6, the scuff resistancewas excellent, a spin rate-lowering effect on shots with a driver (W#1)was obtained, resulting in a satisfactory total distance, and the ballhad an appearance unblemished by pin marks.

1. A method of manufacturing a golf ball having a core and a cover ofone or more layer over the core, wherein an outermost layer of the coveris molded of a thermoplastic material selected from the group consistingof polyurethane, polyurea and mixtures thereof, the method comprising atleast the following steps (1) and (2): (1) treating a surface of thecover with an isocyanate compound; and (2) washing off and physicallyremoving excess isocyanate compound by blasting the cover surface with aspecific substance at high pressure.
 2. The golf ball manufacturingmethod of claim 1 wherein, in step (2), the specific substance that isblasted at high pressure is at least one selected from the groupconsisting of water, alcohol, dry ice, air, sand, vitrified abrasives,plastic abrasives, alumina abrasives, organic abrasives, metalabrasives, and mixtures thereof.
 3. The golf ball manufacturing methodof claim 1 wherein, in step (2), blasting with the specific substance iscarried out at a discharge pressure of at least 3 MPa.
 4. The golf ballmanufacturing method of claim 1 wherein, in step (2), blasting with thespecific substance is carried out at a temperature of at least 5° C. 5.The golf ball manufacturing method of claim 1 wherein, in step (2),washing is carried out for a washing time of at least 10 seconds.
 6. Thegolf ball manufacturing method of claim 1 wherein, when an infraredabsorption spectrum measured by FT-IR/ATR spectroscopy at an outsideportion of the outermost cover layer of the golf ball manufactured bysteps (1) and (2) is plotted as absorbance versus wave number, lettingthe absorbance peak heights near the wave numbers 1512 cm⁻¹, 2280 cm⁻¹and 2840 cm⁻¹ be respectively P₁, Q₁ and R₁, the value Q₁/R₁ is largerthan P₁.
 7. The golf ball manufacturing method of claim 6, wherein thevalue Q₁/R₁ is at least 0.3.
 8. The golf ball manufacturing method ofclaim 6, wherein the value Q₁/R₁ is at least 0.4.
 9. The golf ballmanufacturing method of claim 1, wherein the isocyanate compound is oneor a mixture of two or more selected from the group consisting oftolylene-2,6-diisocyanate, tolyene-2,4-diisocyanate,4,4′-diphenylmethanediisocyanate, polymethylene polyphenylpolyisocyanate, 1,5-diisocyanatonaphthalene, isophorone diisocyanate(including isomer mixtures), dicyclohexylmethane-4,4′-diisocyanate,hexamethylene-1,6-diisocyanate, m-xylylene diisocyanate, hydrogenatedxylylene diisocyanate, tolidine diisocyanate, norbornene diisocyanate,derivatives thereof, and prepolymers formed of said isocyanatecompounds.
 10. The golf ball manufacturing method of claim 1 wherein, instep (10), the isocyanate compound is polymethylene polyphenylpolyisocyanate (polymeric MDI).